This proposal has been designed to approach the general question of how the brain encodes the palatability of a gustatory stimulus. Because decrebrate rats are capable of hedonic judgements about the tastants but are not capable of retaining conditioned taste aversions, it is probable that the brainstem alone is capable of encoding information about palatability, whereas more rostral neural structures may be necessary for modification of these judgements with experience. As a relay in the primary gustatory pathway which also has extensive projections to the forebrain, the parabrachial nucleus of the pons (PbN) may have a significant role in these processes. The three experiments proposed here are designed to: 1) investigate the changes in the electrical activity of the parabrachial nucleus of the pons (PbN) that correlate with the production of a conditioned taste aversion, and 2) investigate the interactions of forebrain mechanisms as they relate to the neural code for taste quality and palatability in the PbN. In three interrelated experiments, the character of the taste response in the PbN will be studied in flaxedilzed rats. In Experiment 1, alterations in the responses to each of the 4 basic tastes will be tested before and after they are paired with an intravenous injection of LiC1. In Experiment 2, the general influence of the forebrain on the conditioned changes in the PbN will be studied in the decrebrate rat under similar experimental conditions. Finally, Experiment 3 is designed to study the specific influence of the gustatory neocortex (known to have extensive reciprocal connections to the PbN) on the response characteristics and conditioned activity of single units in the PbN. This project has broad implications for the understanding of the etiology of eating and taste disorders.